调车作业间歇时应对其他部件进行检查，停留较长时间后再次作业时，应对（）进行试验。
A、自阀机能
B、单阀机能
C、电器性能
D、列车
参考答案：B
单项选择。
There are some in the box.[ ]
A. dog
B. apples
C. fruits
The chairman asked many questions ________ the education of the homeless children in that area.
A．concerned
B．concerning
C．to concern
D．having concerned
of the homeless children in that area.